1. Field of the Invention
The present invention relates to a honeycomb structure. More specifically, the present invention relates to a honeycomb structure capable of improving thermal shock resistance without sacrificing any of light-off performance, catalyst coatability, and strength.
Cordierite ceramics shows low thermal expansion and has excellent thermal resistance and thermal shock resistance. Therefore, cordierite ceramics are widely used for a catalyst carrier for carrying an exhaust gas purification catalyst for a high temperature gas filter or an automobile engine by forming into a porous honeycomb shape. That is, honeycomb structures made of cordierite ceramics are widely used as gas filters or catalyst carriers.
It is required to obtain a honeycomb structure particularly more excellent in thermal shock resistance with the tightening of exhaust emission regulations and the improvement of engine performance.
2. Description of Related Art
For improving thermal shock resistance, the means such as reducing the thermal expansion coefficient of a honeycomb structure can be considered. For example, in Patent Documents JP-T-2003-502261, JP-A-2001-205082, JP-A-2000-239059, JP-T-2006-516528, JP-T-2009-520677, and JP-T-2007-507667, technologies to improve thermal shock resistance of a honeycomb structure are described.
In the technologies described in the aforementioned Patent Documents JP-T-2003-502261, JP-A-2001-205082, JP-A-2000-239059, JP-T-2006-516528, JP-T-2009-520677, and JP-T-2007-507667, there are a problem of reduction of light-off performance due to lower porosity of a honeycomb structure, and a problem of deterioration of catalyst coatability by lower porosity and smaller pore size. The light-off performance means a temperature property of the catalyst loaded on the honeycomb structure exhibiting the purification performance. In the technologies described in the aforementioned Patent Documents JP-T-2003-502261, JP-A-2001-205082, JP-A-2000-239059, JP-T-2006-516528, JP-T-2009-520677, and JP-T-2007-507667, there may be a problem of reducing strength due to higher porosity of a honeycomb structure, and a problem of rise of pressure loss of a honeycomb structure due to the limitation of practically usable cell structure resulted by reduced strength.
In a conventional honeycomb structure, thermal shock resistance and the aforementioned performances could not be satisfied at the same time. That is, in a conventional honeycomb structure, in order to improve thermal shock resistance, any of light-off performance, catalyst coatability, strength, and pressure loss is sacrificed.